Fuel metering system



United States Patent 2,712,928 Patented July 12, 1955 fllicc 2,712,928FUEL METEREJG SYSTEM Application November 19, 1949, Serial No. 128,349 7Claims. (Cl. 261-36) The present invention relates to a fuel system forinternal combustion engines, particularly engines of the small portabletype.

Although the volumetric efficiency of any internal combustion enginegradually decreases throughout most of the engine operating range,particularly at higher eng ne speeds, this factor is usually not ofserious importance, particularly on engines equipped with the fioat typecarburetor which inherently meters the fuel directly in response to themass air flow to the engine. The float type carburetor, however, israther unsatisfactory for small portable engines used on equipment whichis inverted or turned to various off-level positions during operation.For this type of equipment, a fuel system in which the fuel is meteredand delivered to the engine under positive pressure is preferred, butthe relatively high cost of such systems for small engines and thefailure of some or" these systems to respond to changes in volumetriceihciency has prevented their widespread use on this type of engine,which often has rather low volumetric efficiency at the higher speeds.It is, therefore, one of the principal objects of the present inventionto provide a relatively simple metering system for small internalcombustion engines in which fuel is metered and delivered to the enginesunder positive pressure.

Another object of the invention is to provide a pressure type fuelsystem designed especially for small engines in which the volumetriceiliciency decreases appreciably with increases in engine speed.

Further objects and advantages of the invention will become apparentfrom the following description and accompanying drawing, in which isshown a schematic View of our fuel system, the elements thereof beingrearranged to more clearly show their functional relationship to oneanother.

Referring more specifically to the drawing, numeral 2 designates themain body of the fuel metering device, 4 designates an induction passagein the main body, 6 an air inlet, 8 a mixture outlet, and it) a throttlevalve mounted on a throttle valve shaft 12 in said induction passage. Apump generally shown at numeral 14 is provided to deliver fuel at asubstantially constant pressure from a tank (not shown) to the meteringunit and consists of fuel inlet and outlet check valves 16 and 18,respectively, a fuel chamber 2i), a flexible dia phragm 21, a calibratedspring 22 for urging the diaphragm in the fuel delivery direction, and alinkage 23 operatively connecting said diaphragm to a cam or the like(not shown) for actuating the pump. In the operation of the pump,downward movement of diaphragm 21 draws fuel from the tank through valve16 into chamber 26 and upward movement of the diaphragm under thepressure of spring 22 feeds the fuel through valve 18 to member 24containing a filter element or strainer 25.

After passing through the member 24, the fuel flows through conduits 26and 28' to a pressure control unit 39' consisting of a chamber 32 forunmetered fuel and a chamber 34 for metered fuel separated from oneanother by a flexible diaphragm 36 which carries a valve 38 forcontrolling the inlet to a fuel return line 40 connecting chamber 32with the pump inlet or fuel tank. Diaphragm 36 is urged in the directionto close the inlet of line 4f! by a calibrated spring 42 reactingbetween said diaphragm and a fixed wall of chamber 34. The fuel, onentering chamber 32 from the pump, tends to move diaphragm 36 and valve33 away from the inlet to line 40 and when the pressure in the chamberreaches a predetermined value, for example about four pounds, valve 38unseats and permits the fuel in excess of that required to maintain thedesired pressure to return through line so to the source, so that asubstantially constant pressure is maintained in chamber 32 and in anoutlet conduit 44 posterior to a metering orifice 46, throughout normaloperation of the fuel system.

The fuel, on passing through the metering orifice 46 which is controlledby a manually adjustable metering pin 48, is divided into two portions,one portion flowing through conduit Sll of the idle system and the otherportion flowing through conduit 52 of the main discharge system. Themetered fuel flowing from conduit 52 passes through a cut-oil valve 54which is controlled by the throttle valve actuated mechanism tointerrupt the flow of fuel through the main discharge system wheneverthe throttle valve is in closed or partially closed position, as shownin the drawing. A lever tudinally a shaft 58 and valve stem 60, liftingvalve 54 from its seat 62 in opposition to a relatively light spring 64tending to close said valve. The fuel flows through chamber 66, which issealed on the side adjacent shaft 58 by a flexible diaphragm s7 topermit free movement of the shaft through said chamber, and thencepasses through a conduit 68 to fuel discharge unit 70 which consists ofa chamber 72 for metered fuel and a chamber 74 for unmetered fuel, saidchambers being separated by a flexible diaphragm 76 carrying a valvemember 78 and urged in the direction to seat said valve member over theentrance to a discharge nozzle Si) by a caliof chamber 74. The fuel, onentering chan ber 72, tends to move diaphragm 76 and valve 78 in thedirection to open the entrance to discharge nozzle 80 which delivers thefuel to the induction passage 4 on the engine side of the throttlevalve. The unmetered fuel is transmitted to chamber '74 through conduit84 which connects said chamber with conduit 40 which in turn isconnected with the pump inlet or fuel tank. The two units 3% and 7% areconnected by a conduit 86 which transmits the metered fuel pressure inchamber 72 to chamber 34 so that any accidental increase in pressure inchamber 72 will cause a corresponding rise in the pressure throughoutthe system to maintain the desired metering head across orifice 46.

The fuel in conduit fill of the idle system passes through a meteringorifice fill controlled by a manually adjustable metering pin 92 andflows t rough conduit 94 into discharge chamber 72 and thence throughthe discharge nozzle 3i into the induction passage for supplying fuel tothe engine for idling. The idling system remains in full effectthroughout the entire operation of the engine and supplements the maindischarge system at all times While said main system is in operation.

A priming system is also included in the present metering unit andconsistsof a cylinder 199 in which is mounted a reciprocable piston 162urged in the direction to discharge fuel bya spring 194. The piston'ismanually actuated through a rod1ll6 and-handle 196 secured to the end ofsaid rod. The cylinder 10% is connected thence flows through conduit 52V mentioned diaphragm with chamber 32 of the fuel metering unit 30 byconduits 110 and 110', check valve 112 and a chamber 114 "and with theinduction passage on the engine side of a When the handle is released,spring 104 urges piston the fuel from cylinder 1% 116 and port 118, forstarting a cold 102 downwardly, discharging through chamber 114, checkvalve giving an excessively rich mixture engine.

In the operation of the present metering device, the fuel is deliveredby pump 14 through member 24, conduits 26 and 28 to chamber 32 adjacentdiaphragm 36 which regulates the pressure in said chamber to maintain itat a substantially constant value. If the pump should deliver an excessamount of fuel so that there would be a tendency for the pressure inchamber 32 to increase, valve 38 carried by diaphragm 36 moves away fromthe entrance to conduit 40, permitting the excess fuel to return to thetank or pump inlet. The unit 30 maintains a constant pressure in conduit44 so long as the pressure in the system and posterior to the meteringorifice remains substantially constant. If there should be an increasein pressure in the system posterior to the metering orifice, theincrease in pressure is transmitted to chamber 34 through conduit 86,urging diaphragm 36 toward closed position and thereby increasing thepressure in chamber 32 so that a substantially constant head ismaintained across the normally fixed metering orifice 46 to provide asubstantially constant fuel delivery to the engine. As the throttlevalve is opened, the cut-off valve 54 is opened immediately tosubstantially its full capacity so that it has little effect thereafteron the quantity of fuel delivered to the engine.

through valve 54 and conduit 68 to chamber 72 from which it dischargesinto the induction passage through nozzle 80. When the throttle valve isagain closed and the engine is idling, the fuel flows at a constant ratethrough conduit 50, orifice 90 and conduit 94 into chamber 72 anddischarges through nozzle 80 into the induction passage.

Although only one embodiment of our fuel metering device has been shownand described herein, modifications and various arrangements of theelements thereof may be made to suit requirements.

We claim:

1.. A fuel metering device for an engine having an induction system,comprising an unmetered fuel chamber, a metered fuel chamber, adiaphragm separating said chambers, a second metered fuel chamber, asecond unmetered fuel chamber, a diaphragm separating said secondchambers, a conduit adapted to connect the first unmetered fuel chamberwith a source of fuel under pressure, a conduit connecting the firstunmetered fuel chamber with the second metered fuel chamber and having ametering orifice therein, a passage connecting said second metered fuelchamber with said induction system, a passage adapted to connect saidfirst unmetered fuel chamber with the source of fuel for returningexcess fuel delivered to said chamber, a valve actuated by said firstmentioned diaphragm for controlling said second mentioned passage, and avalve actuated by said second for controlling said first mentionedpassage.

I 2. A fuel metering device for an engine having an induction systemwith a throttle therein, comprising an unmetered fuel chamber, 'ametered fuel chamber, a diaphragmseparatingsaid chambers, a secondmetered fuel chamber, a second unmetered fuel chamber, a diaphragmseparating said second chambers, a conduit adapted to connect the firstunmetered fuel chamber with a pump, a conduit connecting the firstunmetered fuel chamber with The fuel the second metered fuel chamber andhaving a metering orifice therein, a passage connecting said secondmetered fuel chamber with said induction system, a passage adapted toconnect said first mentioned fuel chamber with the inlet side of saidpump for returning excess fuel delivered to said chamber, aspring-loaded valve actuated by said first mentioned diaphragm forcontrolling said second mentioned passage, and a spring-loaded valveactuated by said second mentioned diaphragm for controlling said firstmentioned passage.

3. A fuel metering device for an engine having an induction system witha throttle valve therein, comprising an unmetered fuel chamber, ametered fuel chamber, a diaphragm separating said chambers, a secondmetered fuel chamber, a second unmetered fuel chamber, a diaphragmseparating said second chambers, a conduit adapted to connect the firstunmetered fuel chamber with a source of fuel under pressure, a conduitconnecting the first unmetered fuel chamber with the second metered fuelchamber and having a metering orifice therein, and a fuel cut-off valvedownstream from said orifice adapted to be closed only when the throttlevalve is in closed or nearly closed position, a passage connecting saidsecond metered fuel chamber with said induction system, a passageconnecting said first unmetered fuel chamber with the source forreturning excess fuel deliverd to said chamber, a valve actuated by saidfirst mentioned diaphragm for controlling said second mentioned passage,a valve actuated by said second mentioned diaphragm for controlling saidfirst mentioned passage, springs urging each of said diaphragms in thedirection to close said valves, and a passageway for idling fuelconnecting the first unmetered fuel chamber with the second metered fuelchamber and adapted to provide a constant flow of fuel throughout theoperation of said engine.

4; A fuel metering device for small engines having an induction passagewith a throttle therein, comprising an unmetered fuel chamber, a meteredfuel chamber, a diaphragm separating said chambers, a second meteredfuel chamber, a second unmetered fuel chamber, a diaphragm separatingsaid second chambers, a conduit adapted to connect the first unmeteredfuel chamber with a pump, a conduit connecting the first unmetered fuelchamber with the second metered fuel chamber and having a meteringorifice therein and a fuel cut-ofi valve downstream from said orificeadapted to be closed only when the throttle is in closed or nearlyclosed position, a passage connecting said second metered fuel chamberwith said induction passage on the engine side of the throttle valve, apassage connecting said first unmetered fuel chamber with the inlet sideof said pump, a valve actuated by said first mentioned diaphragm forcontrolling said second mentioned passage, a valve actuated by saidsecond mentioned diaphragm for controlling said first mentioned passage,a spring urging each of said diaphragms in the direction to close saidvalves in opposition to the fuel pressure in the first unmetered and thesecond metered fuel chambers,.and a passageway for idling fuelconnecting the first unmetered fuel chamber with the second unmeteredfuel chamber and being adapted to deliver a constant supply of fuelthroughout the operation of the engine.

S. A fuel metering device for an engine having an in- V duction systemcomprising an unmetered fuel chamber,

a metered fuel chamber, a diaphragm separating'said chambers, a secondmetered fuel chamber, a second unmetered fuel chamber, a diaphragmseparating said second chambers, a conduit adapted to connect the firstunmetered fuel chamber with a source of fuel under pressure, a conduitconnecting the first unmetered fuel chamber with the second metered fuelchamber and having a metering orifice therein, a passage connecting saidsecond i said induction' system, a passage connecting saidfirstunmetered fuel chamber with the source for returning excess fueldelivered to said chamber, a spring loaded valve actuated by said firstmentioned diaphragm for controlling said second men tioned passage, aspring loaded valve actuated by said second mentioned diaphragm forcontrolling said first mentioned passage, a passageway for idling fuelconnecting the first unmetered fuel chamber with the second metered fuelchamber, and a manually actuated pump connected by a conduit with thefirst unmetered fuel chamber and by another conduit with the inductionsystem.

6. A fuel metering device for an engine having an induction system,comprising an unmetered fuel chamber adapted to be connected to a sourceof fuel under pressure, a metered fuel chamber connected to saidunmetered fuel chamber and having a movable Wall, a second metered fuelchamber connected to said first metered fuel chamber, a movable wallseparating said unmetered fuel chamber from said second metered fuelchamber, a passage connecting said first metered fuel chamber with theinduction system, a passage adapted to connect said unmetered fuelchamber with said source of fuel for returning the excess fuel deliveredto said chamber, a valve actuated by said second mentioned movable wallfor controlling said second mentioned passage, and a valve actuated bysaid first mentioned movable Wall for controlling said first mentionedpassage.

7. A fuel metering device for an engine having an induction system,comprising a conduit for supplying fuel from a source under pressure tothe induction system, a normally fixed metering orifice in said conduit,a valve in said conduit anterior to said orifice, a chamber, a movablewall in said chamber responsive to unmetered and metered fuel pressurefor controlling said valve, a valve in said conduit posterior to saidorifice, a second chamber, and a movable wall in said second chamberresponsive to metered and unmetered fuel pressure for controiling saidsecond mentioned valve, whereby a substantially constant fuel flow ismaintained through said orifice throughout normal operation of theengine.

References Cited in the file of this patent UNITED STATES PATENTS

